1. Field
The present disclosure pertains to the field of protocols for computer systems. More particularly, the present disclosure pertains to a new method, system, and apparatus for an credit based flow control in a computer system.
Although the scope of the claimed subject matter is not limited in this respect, it is noted that some embodiments may include subject matter from the following co-pending applications: a first patent application with a Ser. No. of 10/833,963, and with a Title of “Simplified Two-Hop Protocol”, with the inventor Ling Cen.
2. Description of Related Art
Computer systems may allow for connecting nodes with a Point to Point (PtP) network. Typically, a protocol controls the communication within a PtP network. For example, the protocol may be divided into a physical layer, link layer, and a protocol layer. The link layer may provide virtual channel (VC) services via a plurality of VC buffers.
Typically, the size of the VC buffers is designed such that there is no bubble or waste on a physical link when packets are sent between the nodes. Various factors affect the size of the link layer buffers, such as, round trip flight time, I/O delay, link buffer delay and multi-node arbitration delay. Thus, the link buffer's size is based on the average round trip delay from the transmission of a unit to the return of a credit. Therefore, each VC buffer for a physical link is sized according to the round trip delay (as exhibited in FIG. 1). However, this is very inefficient. For example, a system would utilize 53,280 bits at each node for a typical configuration of five VCs per direction, 144 bit link unit, 60 entry receiver buffer and 10 entry transmit buffer. The number 53,280 was determined by adding the memory requirement for the receiver of [5 (# of VCs)×64 ×144) to the transmitter of [5 (# of VCs)×10×144.